I have used the "temporary frequency change" method in the past and it works for me; usually along the lines of BackPacker's radio call.
I was taught it's always a good idea to call up any nearby airfields, controlled or uncontrolled, along your route in order to gain traffic information, weather or any other pertinent details. My call usually is along the lines of a typical TPAIR call, adding at the end "will be passing through your overhead/x miles abeam North/South/East/West in x minutes, will report crossing the overhead/abeam the field". Certainly any units I've used this with seem very appreciative of this. Especially useful if you are going anywhere near parachuting sites or if the airfield in question is busy. Then once you're past the airfield you can change back to the LARS/FIR provider you were originally using.
Smithy.